Electrical generator or motor structure – Non-dynamoelectric – Charge accumulating
Reexamination Certificate
2000-06-12
2003-02-25
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Charge accumulating
C318S135000, C318S116000
Reexamination Certificate
active
06525446
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mechanism and a method for driving an electrostatic actuator. In particular, the present invention relates to a mechanism for driving an electrostatic actuator which enables precise positioning and control of retention rigidity (ratio of positional restoration force to positional deviation) of the electrostatic actuator, and to a method for driving the electrostatic actuator.
2. Related Background Art
Various types of electrostatic actuators are disclosed in recent years. The electrostatic actuator is advantageous in (1) its high efficiency without causing loss, and (2) its simple structure constituted only of electrodes, being suitable for miniaturization.
FIG. 9
shows an electrostatic actuator disclosed in Japanese Patent Publication No. 6-101938. In
FIG. 9
, stator
1001
comprises an insulative substrate, and driving electrodes
1002
formed on the surface thereof. Traveler
1003
constituted of a dielectric material is held with a clearance by a holding means (not shown in the drawing) to be movable in the directions shown by arrow marks a and b in the drawing. Driving circuit
1004
applies a voltage to driving electrodes
1002
provided on the surface of stator
1001
. Driving circuit
1004
outputs three phases of driving voltages: &PHgr;A(
1005
), &PHgr;B(
1006
), and &PHgr;C(
1007
). Each of the phases is connected successively to driving electrodes
1002
as shown in FIG.
9
.
FIGS. 10A and 10B
show the timing of voltage application by driving circuit
1004
to the electrodes.
FIG. 10A
shows application of pulse voltage of (0/+V) V of the respective phases (to the respective electrodes).
FIG. 10B
shows application of AC voltage of (+V/−V) V thereto. The application of the pulse voltage as the phases of &PHgr;A(
1005
), &PHgr;B(
1006
), and &PHgr;C(
1007
) as shown in
FIG. 10A
generates an electric field moving in the direction of the arrow mark a (the abscissa t representing the time). The moving electric field induces electric charge in traveler
1003
to exert a driving force to traveler
1003
to follow the moving electric field with a lag. Similarly, the application of pulsed voltage exerts a driving force to the traveler
1003
. To drive the traveler in the reverse direction (the arrow b direction), the phase order of the applied voltage is reversed. This reversal can be conducted by exchanging two of the three voltage-phases.
FIG. 11
shows an electrostatic actuator disclosed in Japanese Patent Publication No. 7-112354. In
FIG. 11
, the parts
2001
-
2007
corresponds to the parts
1001
-
1007
in FIG.
9
.
FIG. 12
illustrates the traveler of the electrostatic actuator shown in FIG.
11
. Traveler
2003
comprises driven electrodes
2008
which are arranged at regular intervals on the face confronting the stator and are kept at a fixed potential. This type of electrostatic actuator is driven by change of electrostatic capacity between the traveler and the stator, which is caused by displacement of the traveler. The voltage is applied to driving electrodes
2002
in such a pattern as shown in
FIGS. 10A and 10B
.
FIG. 13
shows an electrostatic actuator disclosed in Japanese Patent Application Laid-Open No. 6-261558, which floats or levitates the traveler above the stator by a squeeze film effect to remove the friction between the traveler and the stator. In
FIG. 13
, first piezo element
3011
is driven in accordance with the signal from first piezo element control circuit
3013
, and second piezo element
3012
is driven in accordance with the signal from second piezo element control circuit
3014
. In this electrostatic actuator, a squeeze film is formed between traveler
3003
and stator
3001
by driving first piezo element
3011
and second piezo element
3012
to support traveler
3003
by levitation without contact above stator
3001
. Thereby, traveler
3003
is driven by application of a driving voltage to driving electrode
3002
in accordance with signals from electrostatic motor control circuit
3004
similarly as in the aforementioned electrostatic actuator.
However, problems below arise in precise positioning with an electrostatic actuator like those mentioned above. Firstly, in the electrostatic actuator which is driven stepwise by application of driving voltage in a waveform as shown in
FIG. 10A
, high resolution in positioning is not achievable, because the driving step depends on the pattern pitch of the driving electrode and the driving step cannot be made smaller than the pattern pitch, disadvantageously. On the other hand, in the electrostatic actuator which is driven by application of driving voltage in a A waveform as shown in
FIG. 10B
, a control parameter for the actuator is the frequency of driving voltage, namely the speed of actuation. Therefore, for precise positioning with this actuator, a feedback system with a position sensor of high resolution is necessary, which is generally expensive, resulting in high cost of the system. Further, the incorporation of the position sensor into the actuator makes difficult the miniaturization of the actuator. Furthermore, in a conventional electrostatic actuator, the standing position and retention rigidity &kgr; of the traveler can not be set arbitrarily. In the present invention, the retention rigidity &kgr; is a proportionality constant represented by the equation: &kgr;=F/&Dgr;x (where F is the restoring force to restore the traveler to the prescribed standing position, and &Dgr;x is positional deviation of the traveler of the electrostatic actuator from the prescribed standing position). The retention rigidity K is desirably capable of being set arbitrarily since the optimum value thereof depends on the load and the driving conditions.
SUMMARY OF THE INVENTION
The present invention intends to provide a method of driving an electrostatic actuator which does not involve the aforementioned problems of conventional electrostatic actuator and can be provided at a low cost, can be miniaturized readily, and is capable of making the driving step pitch smaller than the pattern pitch of the driving electrode, and also to provide a mechanism of driving the electrostatic actuator.
The present invention intends also to provide a method of driving an electrostatic actuator which enables arbitrary setting of the retention rigidity of a positioned traveler, a mechanism of driving the electrostatic actuator, and an electrostatic actuator employing the method and the mechanism.
An embodiment of the method of driving an electrostatic actuator of the present invention which has a stator having driving electrodes in plural phases and a traveler relatively moved along the stator by application of a driving voltage to the driving electrodes, wherein the driving voltage applied to the driving electrodes is decided according to a voltage function employing as an argument a relative movement position of the traveler on the stator.
Another embodiment of the method of driving an electrostatic actuator of the present invention which has a stator having driving electrodes in plural phases and a traveler relatively moved along the stator by application of a driving voltage to the driving electrodes, wherein the driving voltage applied to the driving electrodes is decided according to a voltage function employing as an argument a retention rigidity with which the traveler is retained at a standing position on the stator.
A still another embodiment of the method of driving an electrostatic actuator of the present invention which has a stator having driving electrodes in plural phases and a traveler moved along the stator by application of a driving voltage to the driving electrodes, wherein the driving voltage applied to the driving electrodes is decided according to a voltage function employing as arguments a position of the traveler and a retention rigidity with which the traveler is retained at a standing position on the stator.
An embodiment of the electrostatic actuator mechanism of the pr
Hirose Futoshi
Yagi Takayuki
Yasuda Susumu
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